Method for beam heating of glass

ABSTRACT

A FINELY DIVIDED SUBSTNCE, SUCH AS A GLASS POWDER OR CRYSTALLINE POWDER, IS TRICKLED FROM AN ELEVATED POSITION INTO A HORIZONTALLY DIRECTED AND HORIZONTALLY FLATTENED LASER BEAM HAVING A WAVE LENGTH GRATER THAN 2.5 $M., PREFERABLY 10.6 $M. THE LASER BEAM MELTS THE POWDER AND THE MOLTEN MATERIAL IS DEPOSITED ON A SLOWLY DOWNWARDLY MOVING BASE CAUSING THE FORMATION OF A ROD OF GLASS OR CRYSTAL ON SAID BASE.

United States Patent 3,756,799 METHOD FOR BEAM HEATING OF GLASS Norbert Neuroth, Mainz-Momhach, Germany, assignor to JENAer Glaswerk Schott & Gen, Mainz, Germany Filed Oct. 13, 1970, Ser. No. 80,298 Claims priority, application Germany, Nov. 3, 1969, P 19 55 175.8 Int. Cl. C03b 5/16, 9/00, 23/20 US. Cl. 65-48 3 Claims ABSTRACT OF THE DISCLOSURE A finely divided substance, such as a glass powder or crystalline powder, is trickled from an elevated position into a horizontally directed and horizontally flattened laser beam having a wave length greater than 2.5 m, preferably 10.6 pm. The laser beam melts the powder and the molten material is deposited on a slowly downwardly moving base causing the formation of a rod of glass or crystal on said base.

wherein dzthe thickness, and S=the pure transmission degree, while 1/k=the depth of penetration of the electromagnetic radiation of the wave length 10.6 m. of the different glasses and glass raw materials. The depth of penetration l/ k. is the distance from the surface at which the intensity of the radiation has been reduced to He. of the intensity of the incident ray. One obtains then values of a few 11111., i.e. already in an extremely thin layer this radiation is completely absorbed. Since one is able to obtain with a CO -gas laser an infrared radiation of a 10.6 m. wave length in a very large capacity (up to 1000 watts), it is possible to heat crystalline materials, glass raw materials, or glass with this radiation source to a molten condition.

The main advantage of this melting method is that the total radiation energy is directly absonbed by the material to be molten and it is not necessary to heat at the same time any crucible material, oven and atmosphere. The exclusive heating operation for the material to be melted makes a crucible dispensible. Accordingly, any impurities which may be caused by the crucible material are eliminated and, furthermore, the melting temperature is not limited by the type of any crucible material.

The drawing illustrates diagrammatically an apparatus which may be used for practicing the method of the present application.

In the drawing:

FIG. 1 illustrates a side elevation view of the device, and

FIG. 2 is a top view of the same.

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Referring to the drawing, the laser beam 1 which is emitted by a commerciallaser apparatus, for instance by a C0, laser, has customarily a circular cross-section. At the start of an operation the laser beam is arranged with its axis substantially horizontal. By employing two cylinder lenses which, for instance, are made of NaCl or germanium, the cross-section of the beam is first reduced in the vertical direction and then is widened in the hori zotital direction.

A convex cylinder lens 2 which, for instance, has a focal length of 10 to 20 cm., is inserted with the longitudinal axis of its cylindrical surface in horizontal direction into the laser beam 1. This lens 2 reduces the thickness of the laser beam in the vertical plane. A concave cylinder lens 3 is inserted with the longitudinal axis of its cylindrical surface disposed in vertical direction into the laser beam. This last mentioned cylinder lens 3 causes a widening of the laser beam in horizontal direction. In this manner it is possible to obtain a beam which in a region at 5 in the vertical plane is relatively narrow and which in the horizontal plane is relatively wide.

The size of the cross-section of the beam is thus determining for the cross-section of the glassy or crystalline article produced.

Above the location where the glassy or crystalline article is to be produced is arranged a powder container 7 with a perforated bottom 8 so that when placed in this container 7 the mixture 4 to be melted trickles in the form of a fine grained powder into the laser beam and is molten at 5. Directly below the beam and in vertical alignment with the container 7 is disposed a base 6 upon which the molten material is deposited. The base 6 is slowly moved downwardly in coordination with the melt ing speed achieved by the laser :beam.

In accordance with a preferred embodiment of the invention the base 6 may be rotated during its downward movement. The laser device and the optic 2,3 are pivotally mounted so that the angle at which the laser beam strikes material to be molten may be varied as desired in order to maintain the efficiency during the melting operation at an optimum value. In this manner a rod of glass or crystal is produced. In the case that a crystal rod is being produced one may, if desired, draw this rod again, or a plurality of times, through the laser beam so that one is able to exploit the effect of the known zone melting method.

The method of the invention may also be practiced in a vacuum or in a protective gas atmosphere in which the base and the powder container are arranged in a chamber which is evacuated or is filled with a gas and in which the laser beam enters this chamber through a window.

Example For the production of a rod consisting of quartz glass, one fills the container 7 with the perforated bottom 8 with quartz crystal powder having a grain size of about m. This powder when discharged through the perforated bottom trickles into the beam of a Co -gas laser which beam passes through a first convex cylinder lens to be reduced in vertical direction and. then passes through a concave cylinder lens in order to be widened in the horizontal direction. This widened laser beam will have in the focal point of the convex. lens a width of about 20 mm. In this region the powder thickles through the beam. Directly below this beam is disposed a fireproof 1 3,75 a v I 4 i ;-v 3 base,.whiehin.accordancmwithuthemelting.speed ofthe melting of said raw material onto a support base powder is moved slowly downwardly. therebelow; and

(d) continuously moving said support base downward- TABLE ly as the molten material accumulates thereon. [Absorption constants of glasses and glass raw materxilals tor the wave 5 2 Th thod ordi to lai 1, i l di g h length 10.6 pm. and dept s of penetration of t e radtauon] p of using a 2 g laser having a Wave length of Absorption Depthofpene- 1() 6 Materials fgflfifi 1115 3. The method according to claim 1, including the step Tum glass (q,uamlglass) i n": 4,840: I 2.1 J of rotat1ng sa1d support base on a substannally vertlcal goditrnslilicatoglesan I 3 -1 5.3 10 BXIS- Bgi si liita t ig lo ss: 23 10 453 "References cled -3 1 UNITED STATES PATENTS 18 1,992,994 3/1935 Delpe'ch 65-134 X 20 3,303,115 2/1967 Nitsche 65DIG. 4 2,852,890 9/1958 Drostet al 65-33 X 3,573,887 4/1971 Mod et al 65-l34 I 3,594,259 7/1971 Coen et al. 65134 m g 3,237,254 3/1966 Hanks et al. 65DIG. 4 1: A method. Of manufacturing glass from a {21W ma: 3 244412 4 1966 R ifi a L 65 DIG 4 terial'in finely-divided condition, comprising the steps 3304403 2/ 9 Harper 4 3415636 12/1968 U U) n 34 4a) Pmducing Substantiallyhmimmallaser 314521178 6/1969 Kieeri 65 1 1ci. 4 a Y P P excess 0f 3,528,484 9/1970 Scharf et al. 65-DIG. 4

(b) 1nsert1ng 1n the path of sand laser beam an optical assembly including a convex cylinder lens having the 25 OTHER REFERENCES axis of its cylindrical surface horizontal and a concave cylinder lens having the axis of its cylindrical surface vertical, thereby causing said laser beam to I assume in the focal region of said convex cylinder lens a vertically narrow and horizontally wide crosssection;

(c) trickling said raw material downwardly through said focal region of the flattened laser beam to cause DIG. 4, 33, 66, 1134 Handbook of Glass Manufacture, vol, II, Foy V. Tooley, pp. 192 to 199, New York, 1961.

FRANK W. MIGA, Primary Examiner 

